The invention relates to a drive control system for an electrical drive having a power section which is at a comparatively high electrical potential, having drive electronics which supply the power section with drive signals, and which receives phase current actual values from this power section, and having a control unit which is at a comparatively low electrical potential and is connected to the drive electronics via a digital communications interface, with DC isolation between the power section and the control unit.
For safety reasons, the high-voltage side of the power section (up to 720 volts) must be safely electrically isolated from the low-voltage side of the control unit (generally approximately 5 volts) in a drive control system such as this. DC isolation is required at some point for this purpose, with the relevant Standards requiring an air gap and creepage distance of, for example, 8 mm. To achieve this, the electrical components which are used must comply with the requirements in these specific Standards.
Present-day solutions for such safe electrical isolation provide this isolation between drive electronics and the power section. A known arrangement of a drive control system such as this is illustrated in the form of a block diagram in FIG. 3.
The power section LT draws its power from an intermediate circuit ZK of a converter (not shown), and provides the three phase voltages for driving a motor M. The drive electronics A produce six drive signals Ux via six respective optocouplers OK (for the sake of clarity, only one such optocoupler is shown by way of example), which are used for driving current valves which are arranged in the power section, in particular a bridge circuit for IGBT transistors. In addition, a further path Ubr such as this may be required for driving a braking chopper.
The respective phase current actual values lactR, lactS, lactT in the three phases R, S, T of the motor M are measured, and are passed via respective isolating amplifiers TV to the drive electronics. In individual cases, only two isolating amplifiers are also provided, since the current in the third phase can be obtained from the two detected phase current actual values. In addition, an isolating amplifier TV is required for detecting the intermediate-circuit voltage Uzk. The drive electronics are connected to the control unit R via a communication interface K.
Thus, according to the prior art, the six or seven (with the braking chopper) optocouplers OK and the isolating amplifiers TV must comply with the requirements for safe electrical isolation. Components such as these are comparatively expensive, as a result of which the fact that a large number of these components that have been mentioned are required means that this approach is highly costly.